A ‘lost world’ of organisms that lived in waterways at least 1.6 billion years ago sheds fresh light on the emergence of complex life.
The ancient marine fossils are believed to represent the earliest known predators on Earth.
They are primitive forms of eukaryotes called protosteroids – specialized cells encased in membranes.
Known as the ‘Protosterol Biota’, the microscopic creatures were found inside a rock at the bottom of the ocean near what is now the Northern Territory in Australia.
Modern eukaryotes include fungi, plants, animals and even single-celled organisms such as amoebae.
Humans can trace their ancestral lineage back to the Last Eukaryotic Common Ancestor (LECA) – which lived more than 1.2 billion years ago.
The Protosterol Biota lived at least one billion years before any animal or plant emerged.
Lead author Dr. Benjamin Nettersheim, now at Bremen University in Germany, said: “Molecular remains of the Protosterol Biota detected in 1.6-billion-year-old rocks appear to be the oldest remnants of our own lineage – they lived even before LECA.
“These ancient creatures were abundant in marine ecosystems across the world and probably shaped ecosystems for much of Earth’s history.
“Modern forms of eukaryotes are so powerful and dominant today that researchers thought they should have conquered the ancient oceans on Earth more than a billion years ago.
“Scientists have long searched for fossilized evidence of these early eukaryotes, but their physical remains are extremely scarce. Earth’s ancient oceans rather appeared to be largely a bacterial broth.
“One of the greatest puzzles of early evolution scientists have been trying to answer is: why didn’t our highly capable eukaryotic ancestors come to dominate the world’s ancient waterways? Where were they hiding?
“Our study flips this theory on its head. We show that the Protosterol Biota were hiding in plain sight and were in fact abundant in the world’s ancient oceans and lakes all along. Scientists just didn’t know how to look for them – until now.”
The Protosterol Biota were certainly more complex than bacteria and presumably larger – although it’s unknown what they looked like, say the Australian National University (ANU) team.
Co-lead author Professor Jochen Brocks, who made the discovery with Dr. Nettersheim, said: “We believe they may have been the first predators on Earth, hunting and devouring bacteria.”
The creatures described in the journal Nature are believed to have thrived until about 800 million years ago.
The end of this period in Earth’s evolutionary timeline is known as the ‘Tonian Transformation’, when more advanced nucleated organisms, such as fungi and algae, started to flourish. But exactly when the Protosterol Biota went extinct is unknown.
Brocks said: “The Tonian Transformation is one of the most profound ecological turning points in our planet’s history.
“Just as the dinosaurs had to go extinct so that our mammal ancestors could become large and abundant, perhaps the Protosterol Biota had to disappear a billion years earlier to make space for modern eukaryotes.”
The findings are based on an analysis of fossilized fat molecules. They possessed a primordial chemical structure that hinted at the existence of early complex creatures that evolved before LECA and had since gone extinct.
Dr. Nettersheim said: “Without these molecules, we would never have known that the Protosterol Biota existed.
“Early oceans largely appeared to be a bacterial world, but our new discovery shows that this probably wasn’t the case.”
It sheds fresh light on the emergence of life on Earth – showing complex multicellular eukaryotes populated the marine biosphere more than a billion years before the Cambrian Explosion 550 million years ago when most modern animal species emerged.
Brocks said: “Scientists had overlooked these molecules for four decades because they do not conform to typical molecular search images.
“But once we knew what we were looking for, we discovered that dozens of other rocks, taken from billion-year-old waterways across the world, were also oozing with similar fossil molecules.”
Dr. Nettersheim completed the analysis as part of his Ph.D. at ANU. The work also involved scientists from France, Germany and the US.
Produced in association with SWNS Talker
Edited by Saba Fatima and Newsdesk Manager
